This invention relates to door latching systems, and particularly to a door lock for use in a fire-rated door, the door lock having a latch blocker actuable by a fusible link to prevent inadvertent or accidental retraction of the latch bolt under fire conditions.
All too often doors are inadvertently or accidentally opened during a fire as a result of spring failure under heat or high velocity fire hose spray. To reduce the likelihood that the fire will spread or increase in intensity, it is necessary to ensure that a closed fire-rated door stay closed by retaining the latch bolt in its door latching position. In that manner, unwanted draft through the doorway closed by the fire-rated door is minimized.
It is well known that biasing springs used in door locks to bias a door latch toward its latching position lose temper when subjected to high spring-annealing temperatures during fire conditions. Loss of spring temper during a fire is particularly troublesome in the case where the door latch is operated by a lever or other unbalanced handle. The eccentric mass of such a lever is often sufficient to exert inadvertently or accidentally a retracting force on the latch bolt when the latch-biasing spring is weakened by exposure to high fire condition temperatures. In addition, levers can be actuated to withdraw the latch bolt inadvertently or accidentally if the lever is struck by a high velocity stream of water from a fire hose operated by fireman.
Temperature-activated latch bolt blocking systems are known, hereinafter referred to as "fusible systems." Operation of conventional fusible systems installed in mortise lock cases and the like have yielded less than satisfactory results for a number of reasons. An improved fire safety door lock of compact size and installable so as to be operative on either hand of door without the need for subsequent conversion or modification would avoid undesirable shortcomings of known fusible systems.
Conventional fusible systems are generally large, bulky apparatus and not easily for conveniently installed in a mortise lock case. Those skilled in the art will appreciate that interior space inside a mortise lock case is at a premium. In addition, conventional fusible systems are typically mounted directly to the case itself and thus not easily converted or otherwise adapted to block the latch bolt if the door providing a housing for the fusible system is itself converted from left-handed to right-handed operation, and vice versa. Such conversion is generally accomplished by removing, inverting, and reinstalling the latch bolt. In such a case, it is generally necessary either to: (1) replace a conventional fusible system for use in a door of one hand with another such system specifically designed for use with a door of the other hand, or (2) modify the latch bolt or other latching components to accommodate the fusible system.
According to the present invention, an improved door lock includes a case, a latch bolt guided within the case between latching and nonlatching positions and yieldably biased by spring means toward its latching position, a blocker member movable between an inoperative position and a blocking position, and fusible means for releasably coupling the blocker member to the latch bolt to hold the blocker member in its inoperative position. The blocker member and the latch bolt are decoupled following exposure of the fusible means to fire condition temperatures. The decoupled blocker member is then gravitationally urged to its blocking position so as to block substantial movement of the latch bolt toward a nonlatching position. Typically, such movement is induced by failure of the spring means during exposure to fire condition temperatures.
In preferred embodiments, the door lock further includes handle means for retracting the latch bolt against the spring means to a nonlatching position within the case. The handle means is a lever and can be expected to induce retraction of the latch bolt once the spring means is weakened by exposure to a spring-annealing temperature during fire conditions. Preferably, the fusible means is made of a material which melts at a temperature below the annealing temperature of the spring means.
The door lock further includes means for suspending the blocker member in its blocking position between the latch bolt and a stop member formed in the case to block movement of the latch bolt toward a nonlatching position. Preferably, the suspending means is defined by a tailpiece extending from a rear face of the latch bolt. In preferred embodiments, the blocker member is formed to include a tailpiece-receiving slot forming first and second interior walls spaced apart in mutually confronting relation thereby permitting one of the interior walls to suspend the blocker member in a blocker position when the door is adapted for left-handed operation, the other interior wall being positioned to suspend the blocker member in its blocking position when the door is adapted for right-handed operation.
One feature of the present invention is the provision of fusible means for releasably coupling a blocker member to the latch bolt itself to hold the blocker member in its inoperative position. In preferred embodiments, the blocker member can take the form of a single deadlocking plate that can fall to a blocking position when actuated during fire conditions. Advantageously, such a plate is compact in size and can be mounted easily in a variety of locations in the lock case.
One other advantage is that the blocker member of the present invention is always operative on either hand of the door without need for conversion or other modification since it is always fixed directly to the latch bolt itself. In the present invention, the latch bolt is the only component that must be reoriented to change a lock from right-handed to left-handed operation (or vice versa). Reorientation of the latch bolt to facilitate the opening of either a left-handed or a right-handed door automatically reorients the blocker member so as to permit the blocker member to fall under gravity to its blocking position without the need for substantial retrofit or service operations.
Another feature of the present invention is the provision of a stop member on the lock case for engaging the decoupled blocker member in its lowered blocking position to prevent inadvertent or accidental withdrawal of the latch bolt. The stop member is easily formed during a stamping operation and is operative whether the door is adapted for left-handed or right-handed operation. In addition, it is very economical to include the stop member as a permanent feature in all lock cases so that the only step necessary to add a temperature-activated latch-blocking system to the lock is to remove the latch bolt, mount the blocker member to the rear face thereof by means of a fusible pin or the like, and reinstall the modified latch bolt. It is unnecessary to modify the case in any way since the stop member is an unobtrusive permanent fixture thereon.
Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.